This invention relates to a scroll type compressor, and more particularly, to a scroll type compressor for an automobile air conditioning system which includes a mechanism for adjusting the displacement of the compressor.
Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Creux discloses such an apparatus which includes two scrolls, each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained angularly and radially offset so that both spiral elements interfit to form a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets increases or decreases, dependent on the direction of the orbital motion. Thus, a scroll type fluid displacement apparatus may be used to compress, expand or pump fluids.
Scroll type fluid displacement apparatus are suitable for use as refrigerant compressors in building air conditioners. In such building air conditioners, thermal control of a room, or control of the air conditioner, is generally accomplished by intermittent operation of the compressor because capacity control mechanisms usually are not provided for the compressors of such air conditioners. Though the energy required for maintaining the room at the desired temperature usually is not large once the desired temperature is first achieved, a relatively large load is required to drive the compressor at least during initial intermittent operation of the compressor and to a lesser extent upon each subsequent actuation of the compressor. This intermittent operation wastefully consumes large amounts of energy.
When conventional scroll type compressors are used in automobile air conditioners, these compressors usually are driven by the automobile engine through an electromagnetic clutch. Once the passenger compartment is cooled to the desired temperature, like building air conditioners, control of the output of the compressor usually is accomplished by intermittent operation of the compressor through the electromagnetic clutch. Since a relatively large load is required to drive the compressor, this large load is intermittently applied by the automobile engine. Accordingly, conventional scroll type compressors for automobile air conditioners also wastefully consume large amounts of energy in achieving and maintaining the desired temperature in the passenger compartment.
Recently, it was recognized that it is desirable to provide a scroll type compressor with a displacement or volume adjusting mechanism to control the compression ratio in response to demand. In a scroll type compressor, control of the compression ratio can be easily accomplished by controlling the volume of the sealed off fluid pockets as disclosed in U.S. Pat. No. 4,505,651 issued 3/19/85 to Kiyoshi Terauchi et al. This application discloses a mechanism for controlling the volume of the sealed off fluid pockets which includes a pair of holes formed through the end plate of one of the scrolls. These holes directly connect intermediate fluid pockets between the scrolls to an intermediate chamber. This intermediate chamber is connected with the suction chamber through another communicating channel or hole. The opening and closing of the communicating channel or hole is controlled by an electrically operated valve member disposed in the intermediate chamber.
While the mechanism disclosed in the above mentioned application controls the compression ratio, and significantly improves the operation of conventional scroll type compressors, this mechanism has not provided a sufficiently wide range of adjustment of compression ratios.